Leica Geosystems GPS Basics - Manual (Page 7)

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GPS Basics -1.0.0en System Overview
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The satellites broadcast two carrier
waves constantly. These carrier waves
are in the L-Band (used for radio), and
travel to earth at the speed of light.
These carrier waves are derived from the
fundamental frequency, generated by a
very precise atomic clock:
• The L1 carrier is broadcast at 1575.42
MHz (10.23 x 154)
• The L2 carrier is broadcast at 1227.60
MHz (10.23 x 120).
The L1 carrier then has two codes
modulated upon it. The C/A Code or
Coarse/Acquisition Code is modulated
at 1.023MHz (10.23/10) and the P-code
or Precision Code is modulated at
10.23MHz). The L2 carrier has just one
code modulated upon it. The L2 P-code
is modulated at 10.23 MHz.
GPS receivers use the different codes to
distingush between satellites. The
codes can also be used as a basis for
making pseudorange measurements
and therefore calculate a position.
GPS Signal Structure
Fundamental
Frequency
10.23 Mhz
L1
1575.42 Mhz
C/A Code
1.023 Mhz
P-Code
10.23 Mhz
L2
1227.60 Mhz
P-Code
10.32 Mhz
ч10
Ч154
Ч120